1. Technical Field
The present invention relates to a shift control device not only for a belt type continuously variable transmission CVT and a toroidal-type continuously variable transmission but also for an automatic transmission including a stepped automatic transmission.
2. Related Art
In a conventional powertrain containing an automatic transmission, a power source such as an engine, a hydraulic transmission element such as a torque converter, and the automatic transmission are connected in these order.
When executing the shift control of the automatic transmission in the powertrain, on the basis of the shift lines which are preset in advance while considering power performance and fuel consumption, a target input speed of the transmission is determined from an accelerator opening and a vehicle speed, and the shift control is executed such that the target input speed of the transmission is achieved, i.e., an actual gear ratio or speed ratio matches a target speed ration which is obtainable by dividing the transmission target input speed by the transmission output rotation speed (vehicle speed).
Meanwhile, the planned shift lines described above is not a universal due to setting the same having the common driving in mind. Thus, in some cases, change in the planned shift lines are required to be executed based on a modified shift line.
Conventionally, a shift or transmission control technique based on the modified shift line has been proposed in Patent Document 1 for example.
The proposed technique addresses a drive or powertrain having an engine, a torque converter, and a continuously variable transmission arranged in the mentioned order, when a large engine braking request is generated during a running state in which the torque converter cannot be locked up (directly connecting the input and output elements) such as in a cold engine operation. In that situation, in place of the shift control based on the planned shift line of the automatic transmission, by changing the shift line, a compulsory downshift in the low gear shift is carried out to thereby realize an engine brake demand of the driver.    Patent Document 1: JP 10-103493 A